There is considerable interest today in the further development of wind power energy. Relatively huge wind motor structures are being erected in selected portions of the world where constantly high velocity wind conditions prevail, and power can be derived therefrom in economically feasible installations. The blades for such machines may be as much as 175 feet in length, and it has been determined that light weight blades formed of a composite synthetic plastic resin-wood construction are well-suited to such applications and are superior in many respects to other materials. For example, such structures possess the necessary strength but do not have the same "fatigue" problems as do blades fashioned from other materials.
For purposes of strength, epoxy resin adhesives have been used to bond the wood layers which form the hollow blade and, as is well known, such adhesive resin materials include both a resin and a hardener or curing agent which when the two components are placed in contact, initiate the hardening process. Because exceptionally strong bonds are required, it is proposed to use such a two component adhesive material, or a compatible material, with suitable inert strengthening filler material, to anchor the alloy metal studs or anchor bolts which are designed to project from the end of the blade, and permit the blade to be securely anchored to the rotor structure.
Studs of the type which are contemplated include an elongate, generally frustoconical plug body with axially spaced projecting radial flanges, fins or threads, and a reduced size, axially extending, attaching end which normally is threaded. Because such projecting studs are subject to huge aerodynamically imposed shear and torsional stresses, the use of a considerable body of filler-adhesive is necessary to bond the studs in properly located positions.
When, in the past, such studs have been adhesively secured in position, problems have been encountered with the entrapment of air in the filler material and the formation of air pockets in the cured material. Further, the considerable heat given off in the exothermic hardening or curing of such bodies of resinous material has exacerbated the problems. Moreover, the location of the studs in the enlarged openings provided in the ends of the composite wood-resin blades has been tricky, and problems have been encountered with loss of the resin material from the openings during the process, to the extent that dams have had to be built to retain the material in the openings.